1. Field of the Invention
This invention relates to a V belt which is mainly used for high load transmitting in a dry type transmission. The V belt according to the present invention is usable not only as the V belt of a continuously variable transmission for motor vehicles but also as the V belt of a continuously variable or uncontinuously variable transmission for vehicles loaded with an engine, such as agricultural machines and civil engineering machines. Also, it is most suitable for a V belt for high load of general industrial machines to be driven by electric motors. Furthermore, it can be used as a belt for transportation or printing by utilizing the upper surface of its block.
2. Description of the Prior Art
For a transmission for running of a motor vehicle, a gear type transmission or an oil pressure type transmission is used. As a transmission having merits of both gear type and oil pressure type, development of a belt type continuously variable transmission with superior workability and less fuel expenses is in progress. This belt type continuously variable transmission comprises at least two pulleys which are variable in the width of grooves and fitted to a driving shaft and driven shafts and a V belt wound round at least two pulleys. Under this construction, continuous variations of speed are effected by varying the rotation pitch diameter by regulating the width of grooves.
These belt type continuously variable transmissions are available in two kinds. One is a wet type transmission using a metallic V belt (Japanese Patent Application Publication Gazette No. 55-6783, for example) and the other is a dry type transmission using a rubber V belt (Japanese Utility Model Application Publication Gazette No. 32-10408, for example). In general, variable transmission drive pulleys are composed by metallic materials, such as cast iron, steel, aluminum alloy, etc., and therefore metallic V belts must be used in lubricating oil to prevent overheating at the frictional surface and wear. However, rubber V belts are free from such trouble and therefore advantageous in the aspects of cost and maintenance.
A transmission for running of motor vehicles is required to have ability to transmit very high torque, for example, when the maximum torque of 1,000 cc engine is transmitted by a rubber V belt, a V belt must stand the lateral pressure force of around 20 Kg/cm.sup.2. However, typical rubber V belts in practical use at present are usually used under the condition of less than 4-5 Kg/cm.sup.2 and even rubber V belts for high load cannot be used under the condition of more than 10 Kg/cm.sup.2. This is because the rubber V belt buckles and deforms by high lateral pressure, with the result that it is broken finally by its generation of heat.
In the above-mentioned metallic V belt, the block is not fixed to the metallic load carrier but slides on the metallic load carrier for transmission by compressive force between blocks. It has been suggested to eliminate impact sound between hard blocks and thereby reduce belt noises during running by setting in hard blocks and elastic blocks alternately (Japanese Patent Application Laying Open Gazette No. 56-120848). Such construction of the metallic V belt, however, involves the decrease of the area in which the V belt receives pressure and reduction of anti-lateral pressure property because lateral pressure force applied by the transmission pulley concentrates upon hard blocks due to the difference in the coefficient of elasticity between elastic blocks and hard blocks. Thus, transmitting ability is reduced and wear of the belt (especially wear of blocks) is accelerated due to the increase of slip. In addition, due to deformation and wear of elastic blocks, the fall phenomenon of hard blocks presents itself and the V belt breaks earlier due to wear and damage of the load carrier at the part where it contacts the hard block.
In order to improve fitness of blocks to the pulley groove, it is generally tried to improve the dimensional precision of blocks but this involves an increase in the cost of parts and resultant increase in the cost of a transmission. In view of such demerits in the aspect of cost, such a technique that notches which open at the underside edge of the metallic block are formed so that when lateral pressure force was applied to the slant side surface, elastic deformation is generated on the metallic block and consequently the angle of inclination of the slant side surface is changed has been disclosed (Japanese Patent Application Publication Gazette No. 57-65444). This technique, however, has a disadvantage in that the forward end portion of the notch is cracked.